#     Copyright 2015, Kay Hayen, mailto:kay.hayen@gmail.com
#
#     Part of "Nuitka", an optimizing Python compiler that is compatible and
#     integrates with CPython, but also works on its own.
#
#     Licensed under the Apache License, Version 2.0 (the "License");
#     you may not use this file except in compliance with the License.
#     You may obtain a copy of the License at
#
#        http://www.apache.org/licenses/LICENSE-2.0
#
#     Unless required by applicable law or agreed to in writing, software
#     distributed under the License is distributed on an "AS IS" BASIS,
#     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#     See the License for the specific language governing permissions and
#     limitations under the License.
#
""" Reformulation of subscript into slicing.

For Python2, there is a difference between x[a], x[a:b], x[a:b:c] whereas
Python3 treats the later by making a slice object, Python2 tries to have
special slice access, if available, or building a slice object only at the
end.

Consult the developer manual for information. TODO: Add ability to sync
source code comments with developer manual sections.
"""

from nuitka import Utils
from nuitka.nodes.ConstantRefNodes import ExpressionConstantRef
from nuitka.nodes.SliceNodes import ExpressionSliceLookup, ExpressionSliceObject
from nuitka.nodes.SubscriptNodes import ExpressionSubscriptLookup

from .Helpers import buildNode, getKind
from .ReformulationAssignmentStatements import buildExtSliceNode


def buildSubscriptNode(provider, node, source_ref):
    # Subscript expression nodes.

    assert getKind(node.ctx) == "Load", source_ref

    # The subscript "[]" operator is one of many different things. This is
    # expressed by this kind, there are "slice" lookups (two values, even if one
    # is using default), and then "index" lookups. The form with three argument
    # is really an "index" lookup, with a slice object. And the "..." lookup is
    # also an index loop-up, with it as the argument. So this splits things into
    # two different operations, "subscript" with a single "subscript" object. Or
    # a slice lookup with a lower and higher boundary. These things should
    # behave similar, but they are different slots.
    kind = getKind(node.slice)

    if kind == "Index":
        return ExpressionSubscriptLookup(
            subscribed = buildNode(provider, node.value, source_ref),
            subscript  = buildNode(provider, node.slice.value, source_ref),
            source_ref = source_ref
        )
    elif kind == "Slice":
        lower = buildNode(
            provider   = provider,
            node       = node.slice.lower,
            source_ref = source_ref,
            allow_none = True
        )
        upper = buildNode(
            provider   = provider,
            node       = node.slice.upper,
            source_ref = source_ref,
            allow_none = True
        )
        step = buildNode(
            provider   = provider,
            node       = node.slice.step,
            source_ref = source_ref,
            allow_none = True
        )


        # For Python3 there is no slicing operation, this is always done
        # with subscript using a slice object. For Python2, it is only done
        # if no "step" is provided.
        use_sliceobj = step is not None or Utils.python_version >= 300

        if use_sliceobj:
            return ExpressionSubscriptLookup(
                subscribed = buildNode(provider, node.value, source_ref),
                subscript  = ExpressionSliceObject(
                    lower      = lower,
                    upper      = upper,
                    step       = step,
                    source_ref = source_ref
                ),
                source_ref = source_ref
            )
        else:
            return ExpressionSliceLookup(
                expression = buildNode(provider, node.value, source_ref),
                lower      = lower,
                upper      = upper,
                source_ref = source_ref
            )
    elif kind == "ExtSlice":
        return ExpressionSubscriptLookup(
            subscribed = buildNode(provider, node.value, source_ref),
            subscript  = buildExtSliceNode(provider, node, source_ref),
            source_ref = source_ref
        )
    elif kind == "Ellipsis":
        return ExpressionSubscriptLookup(
            subscribed = buildNode(provider, node.value, source_ref),
            subscript  = ExpressionConstantRef(
                constant   = Ellipsis,
                source_ref = source_ref
            ),
            source_ref = source_ref
        )
    else:
        assert False, kind
